The present invention relates to operating gas discharge lamps and, more particularly, to operating high intensity discharge (HID) lamps at high frequencies Specifically, the method includes enhancing performance of high intensity discharge lamps by operating at frequencies higher than conventionally used in prior art systems, the frequency of operation is based on excited components in the discharge.
HID lamps produce light by striking an electrical arc across electrodes housed inside a fused quartz or fused alumina arc chamber. The chamber encloses specific components such as mercury vapor, metal halide, alkali and rare earth metals which are selected based on the wavelength of the radiant emission of the excited states of the metallic components.
Standard low-pressure sodium lamps have the highest efficiency of all HID lamps, but they produce a yellowish light. High-pressure sodium lamps that produce a whiter light, but efficiency is somewhat sacrificed. Metal halide lamps are less efficient but produce an even whiter, more natural light. High-intensity discharge (HID) lamps, typically require power supplied by either magnetic or electronic ballasts. Magnetic ballasts provide electrical power to the HID lamp during normal steady-state operation typically at power line frequency, e.g. 50-60 Hz and electronic ballasts provide electrical power to the HID lamp typically at a low-frequency, e.g. 120 to 200 Hz square wave, quasi-sine, pure sine wave or rectangular waveform.
High intensity discharge (HID) gas discharge lamps suffer from acoustic resonances when HID lamps are operated at high frequencies, i.e., between a few kHz to about two hundred kHz, depending on the dimensions of the lamp. Acoustic resonance causes the radiant arc within the lamp to gyrate, flicker, and even be extinguished. However, when the lamps are operated at high frequencies, i.e., above the highest acoustic resonance which depends on the dimensions of the lamp (e.g. ˜50 120 kHz for a 400 W metal halide lamp, lamp performance is not adversely affected. Consequently, there are manufacturers of HID electronic ballasts which power the lamp with high-frequency power, at frequencies just beyond the acoustic resonance range. Such ballasts operate typically at frequencies of 100 to 150 kHz. The frequency of high frequency electronic ballasts is conventionally selected to be high enough to avoid acoustic resonances, but not so high as to increase cost and complexity of the ballast circuit.
In lighting applications, even a small increase, e.g. a few per cent in efficiency or luminous flux translates into considerable electrical energy savings.
There is thus a need for, and it would be highly advantageous to have a system and method of enhancing performance of high intensity discharge lamps by operating at a frequency higher than that conventionally used in prior art systems to increase the efficiency of the operation.
The Commission on Color) dm is C.I.E. (Commission Internationale de l'Eclairage, the International based on mixing different proportions of three hypothetical primary colors (e.g. red green and blue) which create the sensation in a human observer, of any color of light. The three “primary” colors are dubbed “X,” “Y” and “Z.” In order to specify color and not brightness, the relative strengths of the three primary colors are denoted by x, y and z. Since x+y+z must add up to 1 (i.e. 100%) providing x and y is sufficient to specify lamp color; the z value is implied Lamp color is represented on a two-dimensional plot of x and y. All possible colors then fall inside a “color triangle” or chromaticity diagram in which the perimeter encompasses spectrally pure colors (e.g. in rainbows and prisms) ranging from red to blue. A chromaticity diagram is shown in FIG. 1. Moving toward the center “dilutes” the color until the ultimately becomes “white”. Specifying the x,y coordinates locates a color on the color triangle. The color points traversed by an incandescent object (e.g. a standard tungsten lamp) as temperature of the lamp filament is raised can be plotted on the CIE Chromaticity diagram as the “Blackbody curve”. A standard incandescent lamp has a filament at a temperature 2700 degrees Kelvin, and therefore by definition a color temperature of 2700 Kelvins.
The Kelvin system for describing lamp color works well for incandescent lamps, since incandescent lamps are nearly black body radiators, their chromaticity coordinates land directly on the Planckian locus in the CIE x,y color space. The Planckian locus is shown in FIG. 1. Gas discharge and fluorescent lamps, which are not incandescent do not generally produce illumination described by a point in color space which lies on the Planckian locus in the chromaticity diagram.
Color of illumination from gas discharge aid fluorescent lamps is described using “correlated color temperature” (CCT), which assigns a color temperature to a color near, but not on, the Planckian locus. Two lamps whose x,y co-ordinates fall one above the blackbody curve and one below could have the same CCT. However, the one above will appear slightly greener, and the one below slightly pinker. The rated CCT of a discharge or fluorescent lamp tube does not completely specify the color of the illumination.
The CIE developed a newer model for rating light sources, called the color rendering index, which is a mathematical formula describing lamp illumination as compared with the illumination provided by a reference source. Color rendering Index (CRI) is a measure of how closely the lamp renders colors of objects compared to the reference standard source. Daylight is considered a standard but then so also is any “blackbody,” i e., any incandescent object, no matter what its temperature. Based on this definition, daylight and all incandescent and halogen sources have CRI of 100 which is the maximum value. For a warm lamp, CRI is a measure of how close to incandescent the color is; for a very cool lamp CEI is a measure of how close to daylight the color is. Lamps with distorted colors have a low CRI. In general, the higher the CRI the more natural the appearance of the source and the richer colors appear. In general, a CRI of less than ˜50 is not considered acceptable in the market.
Luminous flux is a quantitative expression of the brilliance of a source of visible light which is electromagnetic energy within the wavelength range of approximately 390 nanometers (nm) to 770 nm. This quantity is measured in terms of the power emitted per unit solid angle from an isotropic radiator, a theoretical point source that radiates equally in all directions in three-dimensional space.
The standard unit of luminous flux is the lumen (lm). Reduced to base units in the International System of Units (SI), 1 lm is equivalent to 1 candela steradian (cd sr). This is the same as 1.46 milliwatt of radiant power at a wavelength of 555 nm which lies in the middle of the visible spectrum.
Ref: http://en.wikipedia.org/wiki/Correlated_color_temperature,/Planckian_locus
The term “near” as used herein referring to a operating frequency, is within ten per cent of the operating frequency.
The term “atomic” component refers to atoms added into the chamber of a discharge lamp although the atoms are in ionic form as in a compound, e.g. Lithium Iodide.